1. Field
This disclosure is concerned generally with the attachment and growth of yeast cells on inorganic surfaces. Specifically, the disclosure is concerned with providing a porous inorganic support for the immobilization of a controlled population of such cells.
2. Prior Art
The preparation and use of composites consisting of microbes (bacteria, yeast cells, etc.) fixed on the surfaces of support materials is very old and well known. Typically, a film or slime of microbes is allowed to grow over the surfaces of the support. The resultant film provides a biomass which, depending on the microbes involved, can be used in various practical applications. For example, one of the earlier trickling filter fermentation systems involved using wood shavings or other supports as a packing material which was placed in a container such as a barrel. A liquid raw material was allowed to trickle through the packing and, in some cases, air was allowed to pass upward through the packing. As the liquid was circulated with a simple pump, a film of microbes would form on the surfaces of the packing, thereby resulting in a relatively large accumulation of useful biomass which, depending on the type of microbial film (anaerobic or aerobic conditions), could be used to ferment sugars to alcohol (anaerobic) or convert alcohol to acids (aerobic). The latter process could be used to make vinegar. Early trickling filter systems of that type were commonly referred to as Schuetzenbach generators.
Numerous variations of that type of fermenting system are well known. See, for example, U.S. Pat. No. 454,586 to Bachmann which describes a fermenting vat for the fermentation of sugar solutions to a variety of products. The system consists of a flow-through vat containing a porous packing material. In that patent it was pointed out that the fermentation "germs" of a liquid substrate appeared to multiply more rapidly within the pores and on the surfaces of the packing than when the "germs" were freely floating in the liquid.
Other microbe support systems describing the use of high surface area microbe supports are shown in U.S. Pat. No. 2,440,545 (saw dust, alfalfa chops, cut straw, glass beads, stone grit, etc.); U.S. Pat. No. 3,709,364 (use of sand particles for sewage treatment); U.S. Pat. No. 3,402,103 (series of baffles in a flow through reactor upon which bacterial films are formed); and Indian Pat. No. 43542 (use of porous particles of pumice as supports for yeast cells). From a sampling of the prior art, it is quite clear that others have long appreciated certain advantages of using porous, high surface area inorganic materials as supports for microbial films.
While it can be readily appreciated that there exists a relationship between the porosity of a given support material and the useable surface area that the material provides in a given application, we have now found, quite surprisingly, that in the case of porous supports for yeast cells, there exists a range of pore sizes which, vis-a-vis the cell size, provides an extremely large surface but low volume for a high biomass concentration. Details of our findings and the immobilized yeast cell composites resulting therefrom are described in detail herein.